Question: Solve for $x$ and $y$ using substitution. ${-2x-3y = 3}$ ${y = -x-4}$
Explanation: Since $y$ has already been solved for, substitute $-x-4$ for $y$ in the first equation. ${-2x - 3}{(-x-4)}{= 3}$ Simplify and solve for $x$ $-2x+3x + 12 = 3$ $x+12 = 3$ $x+12{-12} = 3{-12}$ ${x = -9}$ Now that you know ${x = -9}$ , plug it back into $\thinspace {y = -x-4}\thinspace$ to find $y$ ${y = -}{(-9)}{ - 4}$ $y = 9 - 4$ $y = 5$ You can also plug ${x = -9}$ into $\thinspace {-2x-3y = 3}\thinspace$ and get the same answer for $y$ : ${-2}{(-9)}{ - 3y = 3}$ ${y = 5}$